An evaluation of the Lost World and Vertical Displacement hypotheses in the Chimantá Massif, Venezuelan Guayana

Aim To document the occurrence of vertical displacements of vegetation in the high plateaus of the Venezuelan Guayana (tepuis) over the last c. 6000 years, and to discuss their significance for the origin of their flora, especially the endemism patterns observed in their flat summits. Two hypotheses have been proposed for the origin of the summit flora. One (the Lost World hypothesis) proposes a long history of evolution in isolation from the surrounding plains, while the other (the Vertical Displacement hypothesis) suggests that vertical movements of vegetation during the Pleistocene glacial‐interglacial cycles would have resulted in floristic mixing within the lowlands, and genetic interchange among plateau summits. Location This work has been conducted on the flat summit of the Churí‐tepui, in the Chimantá massif, at 5°15′ Lat. N and 62°01′ Long. W, around 2250 m altitude. Methods Pollen analysis and radiocarbon dating of two peat outcrops, using modern analogue technique and numerical methods for palaeoecological interpretation were used. Results The replacement of a high‐altitude plant community (a paramoid Chimantaea shrubland) by a lower elevation (< 2300 m) Stegolepis meadow, occurred about 2500 years before present (yr bp ). This vegetation change is inferred to have resulted from a regional climatic shift to higher temperature and moisture. A subsequent decrease in temperature and moisture led to the establishment of present conditions after about 1450 yr bp . Main conclusions The highland vegetation of the tepuis responded to climate shifts with vertical displacements, supporting the hypothesis of vertical mixing. However, a physiographical analysis shows that around half of the tepuis would never have been connected by lowlands. Therefore, both hypotheses are needed to explain the origins of the summit flora in the tepuis.     

The impact of climate change on the physical characteristics of the larger lakes in the English Lake District

1. The larger lakes of the English Lake District have been the subject of intensive scientific study for more than 60 years. Year‐to‐year variations in the weather have recently been shown to have a major effect on their physical characteristics. The area is mild but very wet and the dynamics of the lakes are strongly influenced by the movement of weather systems across the Atlantic. 2. Here, we combine the results of long‐term measurements and the projections from a Regional Climate Model (RCM) to assess the potential impact of climate change on the surface temperature and residence times of the lakes. 3. The RCM outputs used were produced by the U.K. Hadley Centre and are based on the IPCC ‘A2’ scenario for the emission of greenhouse gases. These suggest that winters in the area will be very much milder and wetter by the 2050s and that there will be a pronounced reduction in the summer rainfall. 4. An analysis of the meteorological data acquired between 1940 and 2000 shows that there have been progressive increases in the winter air temperature and in the rainfall which are correlated with the long‐term change in the North Atlantic Oscillation. The trends reported during the summer were less pronounced and were correlated with the increased frequency of anticyclonic days and a decrease in the frequency of westerly days in the British Isles. 5. A simple model of the year‐to‐year variations in surface temperatures showed that the highest winter temperatures were recorded in the deeper lakes and the highest summer temperatures in the lakes with the shallowest thermoclines. When this model was used to predict the surface temperatures of the lakes in the 2050s, the greatest winter increase (+1.08 °C) was observed in the shallowest lake and the greatest summer increase (+2.18 °C) in the lake with the shallowest thermocline. 6. The model used to estimate the seasonal variation in the residence time of the lakes showed that the most pronounced variations were recorded in lakes with a short residence time. Average winter residence times ranged from a minimum of 10 days to a maximum of 436 days and average summer values from a minimum of 23 days to a maximum of 215 days. When this model was used to predict the residence time of the lakes in the 2050s, the greatest winter decrease (−20%) was observed in the smallest lake and the greatest summer increase (+92%) in the lake with the shortest residence time. 7. The results are discussed in relation to trends reported elsewhere in Europe and the impact of changes in the atmospheric circulation on the dynamics of the lakes. The most serious limnological effects were those projected for the summer and included a general increase in the stability of the lakes and a decrease in the flushing rate of the lakes with short residence times.     

Suboptimal thermoregulation in male adders (Vipera berus) after hibernation imposed by spermiogenesis

In ectotherms, the main behavioural option for thermoregulation is the adjustment of daily and seasonal activity to the thermal quality of the environment. While active, ectotherms thermoregulate by shuttling in between thermally differing microhabitat patches. Here, we focused on the question of whether other behavioural or physiological processes could force ectotherms to maintain activity during thermally unfavourable periods, when accurate thermoregulation is impossible. Using laboratory experiments and field data we compared the thermoregulation of male adders ( Vipera berus ) between two periods in spring when (1) only males and (2) also females and juveniles had terminated their winter hibernation. We found that males thermoregulated actively both in the lab and in the field. Accurate thermoregulation was only possible during the second period because of the low thermal quality of the environment. Male adders maintained a lower mean body temperature in the field than in the laboratory within both periods, and in addition their body temperature during the first period was on average 4 °C lower than during the second period. The thermal qualities of the natural basking sites showed a similar pattern. We discuss the results in the context of a potential trade-off between spermiogenesis and thermoregulation, where the benefits of early spermiogenesis coupled with inaccurate thermoregulation are higher than the associated costs. The results support the contention that the earlier spring emergence of the male compared with female adders is explainable by natural selection favouring early initiation of spermiogenesis, and hence sex differences in phenology.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 19–27.     

Optimum prediction of three-way crosses from single crosses in forage maize (Zea mays L.)

Summary Three-way cross means were predicted with formulae involving linear functions of general (GCA) and specific combining ability (SCA) effects estimated from single-cross factorials between genetically divergent populations. Data from an experiment with 66 single-cross and 66 three-way cross forage maize (Zea mays L.) hybrids was used for comparing the prediction formulae. The genotypic correlation (r) between observed and predicted three-way crosses increased with increasing , the weighting factor of SCA effects, for plant height and ear dry matter (DM) content. It displayed slightly convex curves for total and stover DM yield, ear percentage, and metabolizable energy content of stover. For Jenkins' method B, r was considerably less than 1.0 for all traits, indicating the presence of epistasis. The square root of heritability (h) of the predicted means decreased with increasing , the reduction being small with a greater number of test environments. Using the product r·h as a criterion of efficiency, none of the prediction methods was consistently superior and the differences among them were rather small (< 7.5%) for all traits, irrespective of the number of test environments. We recommend evaluating the GCA of a greater number of lines from each parent population in testcrosses with a small number of elite lines from the opposite population. All possible three-way or double crosses between both sets of lines should be predicted by Jenkins's method C. This procedure allows one to select with a higher intensity among the predicted hybrids and thus should increase the genetic gain.Extended version of a paper (Geiger et al. 1986) read at the sixth meeting of the EUCARPIA Section Biometrics in Plant Breeding held at Birmingham, UK, July 28–August 1, 1986     

Ecological aspects of thermoregulation at high altitudes: the case of andean Liolaemus lizards in northern Chile

Summary We document activity field temperatures, daily activity patterns, and extent of thermoregulation in four species of Liolaemus lizards inhabiting at high altitude (above 3500 m) in the Andes of northern Chile. These four species have similar activity field temperature (Tb near 29°C) despite their being distributed at different altitudinal belts. However, conspicuous differences exist between higher-altitude (L. alticolor and L. jamesi) and lower-altitude (L. islugensis and L. ornatus) lizards regarding extent of thermoregulation and activity period. Some differences in morphology, behavior, and patterns of microhabitat occupancy are also apparent among these four species and are seemingly related to the thermal environment to which they are subjected. In comparison to eight low-altitude Liolaemus species in central Chile (Tb near 35°C) the four high-altitude species in northern Chile have lower activity field temperature. The latter is apparently due to the constraints imposed by the harsh Andean thermal environment, a hypothesis supported by the fact that high-altitude Liolaemus lizards under laboratory conditions demonstrate body temperatures that exceed by 5°C or more, those recorded in the field.     

Sublethal effects of aldicarb on the behaviour of Aphis fabae and two clones of Myzus persicae and on the transmission of beet mosaic virus by these aphids

In laboratory experiments treatment of sugar-beet plants with aldicarb stimulated the mobility of Aphis fabae and two clones of Myzus persicae which were susceptible (S) and resistant (R) to carbamate-based insecticides, respectively. On the other hand, the number of aphids probing and the total number of probes made was reduced, and hence the transmission of beet mosaic virus (BMV) was restricted. In outdoor experiments the spread of BMV from aldicarb-treated plants by naturally infesting aphids was also restricted. The number of infected plants decreased with increasing distance from the sources of infection.

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Résumé Des plantes de betterave traitées au laboratoire avec de l'aldicarbe ont stimulé la mobilité d'Aphis fabae et de deux clones de Myzus persicae, l'un sensible et l'autre résistant à des insecticides contenant des carbamates. Par ailleurs, le nombre de pucerons en train de sonder les feuilles ainsi que le nombre total de sondages ont été réduits et ainsi la transmission du virus de la mosaïque de la betterave (BMV) a été limitée. Dans des expériences à l'extérieur, la vitesse de propagation de BMV par des pucerons sur des plantes traitées à l'aldicarbe a été aussi plus limitée. Le nombre de plantes contaminées diminuait avec la distance de la source de contamination.

     

Dendrochronology in Coniferous forests around Lake Rara,West Nepal

In two forest stands, one domonated byAbies spectabilis, and the other byPinus wallichiana-Picea smithiana, 198 cores were taken from 105 conifers in May 1983 and the annual ring widths were measured. The annual ring widths usually had significant similarities between cores taken from the same tree and with cores taken from different trees. these similarities increased with tree size. The climatic change affected the large trees more strongly than it did the small trees. Micro environmental changes, such as canopy gap affected the small trees more strongly. Annual ring widths were also correlated with the annual precipitations at Jumla 30 km south of the plots for a recent 20 year period. A multiple regression analysis between ring width and seasonal precipitation showed that the growth ofA. spectabilis was correlated primarily with the rain from May to August and secondarily with that from September to December in the previous year.     

Linear and non-linear regression analysis of genotype X environment interactions in pearl millet

Summary Regression analysis was computed on the grain yield of 15 single cross F₁ hybrids of pearl millet (Pennisetum typhoides (Burm.) S. & H.) evaluated in 20 environments at 19 sites in India to assess the nature of genotype X environment interactions. Linear, quadratic, cubic, twoand three-intersecting straight line models were examined for fit. The interactions of six hybrids viz. MH 110, MH 113, MH 114, MH 115, MH 120 and MBH 110 were explained by the linear regression model. The response of the remaining nine hybrids was largely non-linear. The two and three-intersecting straight line models fit better than the quadratic and cubic models and explained non-linearity of response. The two-intersecting straight line models fit for 6 hybrids MH 106, MH 107, MH 112, MH 116, MH 117 and BJ 104. The response of MH 109 was best explained by a three-intersecting straight line model, but there still existed a significant remainder variation. The truncation of environmental range by assuming moving division points was more efficient than the fixed division points for the segmental regression models. The stability of hybrid varieties on the best fitting model has been discussed.     

Structure and function of ferredoxin-NADP+-oxidoreductase

The redox-enzyme ferredoxin-NADP-oxidoreductase has been shown to be activated by light and inactivated in the dark. This review will summarize recent data concerning the biochemical characterization of the enzyme compared to its in-vivo activation. Further-more the mechanism of this activation process is discussed as a conformational change caused by the light-driven proton gradient.Abbreviations cyt cytochrome - fd ferredoxin - FNR1 large form of ferredoxin-NADP-oxidoreductase - FNRox oxidized FNR - FNRred reduced FNR - FNRs small form of FNR - FNRsq FNR-semiquinone